Turbines are devices that generate rotary mechanical power from the energy in a stream of moving fluid. Applications in which turbines may be incorporated include aircraft, watercraft (both marine- and fresh water-based systems), various types of land-craft, and the like. Materials from which turbine components may be fabricated typically include those from a class of materials known as superalloys, which characteristically exhibit desirable chemical and physical properties under the service conditions generally experienced during turbine operation. Superalloys in which the base constituent is an alloy of nickel (Ni), iron (Fe), or cobalt (Co) are of particular interest in such applications because of their ability to withstand the normally high operating temperatures of the turbine service environment. Temperature constraints of such superalloys, particularly with respect to single-crystal nickel-based superalloys, however, limit the use of such superalloys in turbine engines in which extreme temperature conditions may be experienced.
At such extreme temperatures, the superalloys that are used to form the turbine components are highly susceptible to damage from such mechanisms as creep, oxidation, and melting. The application of thermal barrier coatings (TBCs), which are typically formed of a refractory material, to the component surfaces enhances the performance of superalloys at extreme temperature by reducing the temperature at the metal surface. Although such coatings offer some degree of protection, they are subject to undesirable qualities such as chipping, cracking, and spalling.
The problems associated with resistance to oxidation in the turbine service environments as well as the melting points of the construction materials are often exacerbated by state-of-the-art turbine designs, which call for increasingly higher operating temperatures in order to boost turbine efficiency. In advanced design concepts, the surface temperatures of components are expected to exceed the melting points of state-of-the-art superalloys. What is needed, therefore, are turbine components having improved extreme temperature capabilities relating to such parameters as, for example, elevated melting point and oxidation resistance. In particular, new airfoil materials and structures are needed to surpass the existing state-of-the-art superalloys and structures to attain higher engine efficiencies. Due to the high costs associated with materials exhibiting sufficient extreme temperature capabilities, an additional need is cost effectiveness of the component.